The cost pressures in the automotive industry in general, combined with the necessity for an economically efficient production, have given rise to considerations of a modular construction of motor vehicles. In this type of construction, certain components of a vehicle are completely assembled by suppliers to form modules which together with other modules are then assembled into a complete vehicle by the vehicle manufacturer using bolted connections, e.g. in accordance with German Laid Open Publication DE 38 09 456 A1. This manufacturing concept follows the trend of increasingly relocating assembly work to the supplier to reduce, among other things, the storage capacities required by the vehicle manufacturer. The cited publication also describes a rear end module comprising a rear end trim part, the taillight panel provided with openings for the taillight assemblies and the separately mountable bumper.
A modular construction of a vehicle is also disclosed in German Laid Open Publication DE 196 21 451 A1.
This publication describes three typical modules of a motor vehicle. The first module comprises the entire front end. The second module comprises the passenger compartment with the front and rear windshield, including two exterior rear fenders molded thereto. A third module, the rear end module, is inserted therebetween from behind and the top forming a seal when the vehicle is assembled at the vehicle manufacturer's plant. This rear end module comprises the entire trunk with the floor part and possibly a floor well for the spare wheel and, opposite the exterior fenders, sidewalls to which the taillights are mounted, and the front and rear end wall of the trunk. The rear bumper, comprising the bumper flexural member bolted to the two longitudinal members and its cover, also forms part of the rear end module.
In addition to the effect of modular construction on the economic efficiency of vehicle production, the ease with which the modules can be repaired is also important for insurance rate classification. For example, if the modules are too large, i.e. if they include too many components, the entire module must be replaced after a collision. This makes it costly to repair minor damage after an accident.
Today, the repair of vehicles with light to moderate front end collision damage is therefore substantially facilitated by relatively small front end modules in which the front end is divided into components that can be bolted together, i.e.                a front structure comprising the headlight assemblies, the radiator, the hood lock and various other units,        a primary structure for specific energy absorption and        an outer enclosure, e.g. a bumper apron,        
The front structure and the outer enclosure also help absorb energy.
Because the components can be replaced by bolting them into place, costly welding and alignment work is reduced, so that insurers classify these vehicles in lower full collision rate categories.
For rear end structures, the current practice is to use only small modules for specific energy absorption. This rear end module comprises small energy-absorbing deformation elements, so-called crash boxes, which in practice are a part of the rear longitudinal member, as well as the bumper flexural member, which is typically trimmed like a bumper. This rear end module is bolted to the body in the area of the rear longitudinal member.
Such a rear end module is described, for instance, in German Laid Open Application DE 198 31 708 A1.
The invention is based on this type of rear end module.
For space reasons, the so-called rear end middle piece of the body-in-white structure and other rear end components clearly protrude over the bolting surfaces of such a rear end module in longitudinal vehicle direction and thereby prevent energy absorption solely through the crash boxes. Thus, in case of a rear impact, although the longitudinal member is kept free from damage by the boltable rear end module, the rear end middle piece itself is prematurely deformed because of its exposed position.
As a result, undesirable body damage occurs despite the boltable rear end module. This causes costly repairs and has a negative effect on the insurance classification.